JohnD60

I need your ideas.

For the last few track weekends I’ve experienced an intermittent drive line imbalance when driving the car for the first 1/4 mile or so after it cools down. It is definitely in the driveline. Engine runs fine, clutch engages normally, you can still feel and hear the wobble when you are coasting with the clutch disengaged and the frequency changes as the car slows down.

After a short drive things seem to align again and the car runs fine; can be pushed hard with no other symptoms.

Also, the problem only occurs after a track session. Daily street driving, day after day, is fine.

The car has a Fidenza flywheel and a LS7 clutch that are about a year old. Shortly after having the clutch replaced I had a torque tube failure. The complete torque tube assembly was replaced with the 12mm version, a solid bushing in the rear and a rubber bushing up front.

Here’s the kicker. I suspected the front rubber bushing was the problem and paid my local dealer to replace it just last week. They found the bushing was worn and said everything else looked fine. After two sessions this past weekend the wobble returned!

I can not believe a bushing could fail that quickly but I’m at a lost to determine what else could create this type of a problem. Would love to diagnosis the problem before a catastrophic failure but I’m not sure what’s next.

Any ideas or other experiences along these lines?

Thanks

John

davidfarmer

if it's in the driveshaft, or anywhere in front of the trans, you should feel it when revving the engine at a standstill (clutch engaged). If not, it's in the trans or further rearward. You really need to get the car in the air, and run it. Try to determine if it's rpm related (pre trans), or speed related (trans, diff, half shafts, brakes, tires).

I personally think the solid bushings cause the shafts to lose balance FASTER than without them, but it only took me once to toss them. However, it could be a balancer issue, pilot bearing issue, clutch issue, shaft, trans, or simply tire pickup/balance.

0Robert@SPEEDSOUTH

Only rubber/rubber here.

David mentions some good points. Run it through every circumstance you can think of and keep a notepad handy. Its all about isolating your variables at this point.

Unless you're testing, I wouldn't drive it until you have the problem resolved.

gonzalezfj

David has the right answer. If it's the driveshaft, revving the engine at different speeds with the clutch engaged should produce the vibration. If it doesn't, it is probably tire related. If you have another set of wheels and tires (or can borrow one from a friend), put them on and see if the problem disappears.

Imbalance problems that cure themselves with a few minutes of driving are typical of a tire flatspotting when parked hot and working its way back to round again as it rolls for a while.

Best,
Frank Gonzalez

JohnD60

Thanks for the ideas guys. I will do what David outline after the next occurance.

I didn't think about reving it in neutral with the clutch engaged to isolate the Torque Tube. Seems so obvious now that David mentions it........... kicking myself for not thinking of it Sunday afternoon at the track!

I'll let you know what I find.

Thanks again,

John